Ionization balance device with shielded capacitor circuit for ion balance measurements and adjustments

Abstract

In one example, this disclosure describes a circuit and techniques that may be used to measure the ion balance in an ionization balance device ( 10 ). The described circuit comprises a capacitor ( 22 ) that includes two conductors ( 23, 24 ), wherein a first one ( 23 ) of the conductors is exposed to the output of the ionization device, and the second one ( 24 ) of the conductors is shielded from the output of the ionization device. The first conductor may accumulate charge so as to quantify the output of the ionization balance device. A switch ( 29 ) may be used to discharge the first conductor at periodic intervals in order to measure the accumulated charge on the first conductor, and signal processing may be performed on this discharge measurement in order to generate feedback that can be used to control and adjust the output of an ion source.

The invention claimed is: 
     
       1. An ionization balance device for use with a stream of ions flowing away from the ionization balance device and in a direction generally toward a target area, wherein the stream of ions is comprised of a plurality of ions, the ionization balance device comprising:
 an ion source configured to emit the plurality of ions; 
 a capacitor including a first conductor and a second conductor,
 wherein the first conductor is configured to be exposed to at least a portion of the plurality of ions; and 
 wherein the second conductor is configured to be shielded from the at least a portion of the plurality of ions and to output a first signal; and 
 
 a signal conditioning circuit coupled to the second conductor of the capacitor, wherein the signal conditioning circuit is configured to receive the first signal and to output a second signal indicative of ion balance based, at least in part, upon the first signal, and wherein the signal conditioning circuit includes at least one peak and hold detector. 
 
     
     
       2. The ionization balance device of  claim 1 , wherein the first conductor is further configured to shield the second conductor from the at least a portion of the plurality of ions. 
     
     
       3. The ionization balance device of  claim 1 , wherein the capacitor comprises:
 an outer conductor comprising the first conductor; and 
 an inner conductor comprising the second conductor. 
 
     
     
       4. The ionization balance device of  claim 3 , wherein the capacitor comprises a dielectric between the outer conductor and the inner conductor. 
     
     
       5. The ionization balance device of  claim 3 , wherein the capacitor comprises one of:
 a cylindrical capacitor, 
 a rectangular capacitor, and 
 an oval capacitor. 
 
     
     
       6. The ionization balance device of  claim 1 , wherein the signal conditioning circuit is configured to generate:
 a third signal proportional to a positive charge on the capacitor; and 
 a fourth signal proportional to a negative charge on the capacitor. 
 
     
     
       7. The ionization balance device of  claim 1 , wherein the signal conditioning circuit further comprises at least one of:
 an amplifier, and 
 a low pass filter. 
 
     
     
       8. The ionization balance device of  claim 6 , wherein the second signal of the signal conditioning circuit is based, at least in part, upon a difference between the third signal and the fourth signal. 
     
     
       9. The ionization balance device of  claim 8 , further comprising a control unit configured to receive the second signal of the signal conditioning circuit and generate control signals for the ion source in order to change the ion balance. 
     
     
       10. The ionization balance device of  claim 1 , further comprising a switch, wherein the first conductor is configured to accumulate the at least a portion of the plurality of ions when the switch is open, and wherein the capacitor is configured to discharge accumulated charge when the switch is closed. 
     
     
       11. The ionization balance device of  claim 10 , wherein the switch is configured to be opened and closed at periodic intervals to generate signals indicative of ion balance. 
     
     
       12. The ionization balance device of  claim 10 , wherein the capacitor is configured to output a pulse when the switch is closed, wherein the pulse defines:
 a magnitude that is proportional to an excess charge accumulated on the first conductor; and 
 a direction that defines whether the excess charge is a positive charge or a negative charge. 
 
     
     
       13. The ionization balance device of  claim 10 , further comprising a resistor sharing an end terminal with the capacitor, wherein the capacitor is configured to discharge through the resistor when the switch is closed. 
     
     
       14. The ionization balance device of  claim 13 , wherein the resistor defines a resistance less than approximately 10 megaOhm. 
     
     
       15. The ionization balance device of  claim 13 , wherein the capacitor is a first capacitor, the ionization balance device further comprising a second capacitor positioned in parallel with the resistor, the parallel combination of the resistor and the second capacitor being in series with the first capacitor. 
     
     
       16. The ionization balance device of  claim 15 , wherein the second capacitor comprises the second conductor of the first capacitor and a third conductor. 
     
     
       17. The ionization balance device of  claim 16 , wherein the third conductor is configured to be shielded from the at least a portion of the plurality of ions. 
     
     
       18. The ionization balance device of  claim 1 ,
 wherein the second signal is substantially insensitive to any external electromagnetic fields that are not generated by the plurality of ions. 
 
     
     
       19. The ionization balance device of  claim 18 , wherein the capacitor is a first capacitor, the ionization balance device further comprising:
 a second capacitor comprising the second conductor of the first capacitor and a third conductor; 
 a resistor positioned in parallel with the second capacitor, the parallel combination of the resistor and the second capacitor being in series with the first capacitor; and 
 a switch, wherein the first conductor is configured to accumulate the at least a portion of the plurality of ions when the switch is open, and wherein the first capacitor is configured to discharge accumulated charge when the switch is closed. 
 
     
     
       20. A circuit configured to measure ion balance of an ion source, wherein the circuit is for use with a stream of ions flowing away from the ion source and in a direction generally toward a target area, wherein the stream of ions is comprised of a plurality of ions, the circuit comprising:
 a first capacitor including a first conductor and a second conductor,
 wherein the first conductor is configured to be exposed to at least a portion of the plurality of ions, and 
 wherein the second conductor is configured to be shielded from the at least a portion of the plurality of ions and to output a first signal; 
 
 a second capacitor comprising the second conductor of the first capacitor and a third conductor; 
 a resistor positioned in parallel with the second capacitor, the parallel combination of the resistor and the second capacitor being in series with the first capacitor; 
 a switch, wherein the first conductor is configured to accumulate the at least a portion of the plurality of ions when the switch is open, and wherein the first capacitor is configured to discharge accumulated charge when the switch is closed; and 
 a signal conditioning circuit coupled to the second conductor of the first capacitor, wherein the signal conditioning circuit is configured to receive the first signal and to output a second signal indicative of ion balance based, at least in part, upon the first signal, and wherein the first signal is based on the accumulated charge discharged by the first capacitor, and wherein the signal conditioning circuit includes at least one peak and hold detector. 
 
     
     
       21. The circuit of  claim 20 , wherein the first conductor is configured to shield the second conductor from the at least a portion of the plurality of ions. 
     
     
       22. The circuit of  claim 20 , wherein the first capacitor comprises:
 an outer conductor comprising the first conductor; and 
 an inner conductor comprising the second conductor. 
 
     
     
       23. The circuit of  claim 22 , wherein the first capacitor comprises a dielectric between the outer conductor and the inner conductor. 
     
     
       24. The circuit of  claim 22 , wherein the first capacitor comprises one of:
 a cylindrical capacitor, 
 a rectangular capacitor, and 
 an oval capacitor. 
 
     
     
       25. The circuit of  claim 20 , wherein the signal conditioning circuit is configured to generate:
 a third signal proportional to a positive charge on the first capacitor; and 
 a fourth signal proportional to a negative charge on the first capacitor. 
 
     
     
       26. The circuit of  claim 20 , wherein the signal conditioning unit comprises at least one of:
 an amplifier, and 
 a low pass filter. 
 
     
     
       27. The circuit of  claim 25 , wherein the second signal of the signal conditioning unit is based, at least in part, upon a difference between the third signal and the fourth signal. 
     
     
       28. The circuit of  claim 27 , further comprising a control unit configured to receive the second signal of the signal conditioning circuit and generate control signals to the ion source to change the ion balance. 
     
     
       29. The circuit of  claim 22 , wherein the switch is configured to be opened and closed at periodic intervals to generate signals indicative of ion balance. 
     
     
       30. The circuit of  claim 22 , wherein the circuit is configured to output a pulse when the switch is closed, wherein the pulse defines:
 a magnitude that is proportional to an excess charge accumulated on the first conductor; and 
 a direction that defines whether the excess charge is a positive charge or a negative charge. 
 
     
     
       31. The circuit of  claim 22 , wherein the resistor defines a resistance less than approximately 10 megaOhm. 
     
     
       32. The circuit of  claim 22 , wherein the third conductor is configured to be shielded from the at least a portion of the plurality of ions. 
     
     
       33. A circuit configured to measure ion balance of an ion source, wherein the circuit is for use with a stream of ions flowing away from the ion source and in a direction generally toward a target area, wherein the stream of ions is comprised of a plurality of ions, the circuit comprising:
 a first capacitor including a first conductor and a second conductor,
 wherein the first conductor is configured to be exposed to at least a portion of the plurality of ions, and 
 wherein the second conductor is configured to be shielded from the at least a portion of the plurality of ions and to output a first signal; 
 
 a second capacitor comprising the second conductor of the first capacitor and a third conductor; 
 a resistor positioned in parallel with the second capacitor, the parallel combination of the resistor and the second capacitor being in series with the first capacitor, wherein the resistor defines a resistance less than approximately 10 megaOhm; and 
 a signal conditioning circuit coupled to the second conductor of the first capacitor, wherein the signal conditioning circuit is configured to receive the first signal and to output a second signal indicative of ion balance based, at least in part, upon the first signal, and wherein the signal conditioning circuit includes at least one peak and hold detector. 
 
     
     
       34. The circuit of  claim 33 , wherein the resistance is between 100 kiloOhm and 10 megaOhm. 
     
     
       35. The circuit of  claim 33 , further comprising a switch, wherein the first conductor is configured to accumulate the at least a portion of the plurality of ions when the switch is open, and wherein the capacitor is configured to discharge accumulated charge when the switch is closed.